Benign Tumours of the Ovary

Structure of ovaries:
The ovaries are covered on the outside by a layer of simple cuboidal epithelium called germinal (ovarian) epithelium. This is actually the visceral peritoneum that envelops the ovaries. Underneath this layer there is a dense connective tissue capsule, the tunica albuginea. The substance of the ovaries is distinctly divided into an outer cortex and an inner medulla. The cortex appears more dense and granular due to the presence of numerous ovarian follicles in various stages of development. Each of the follicles contains an oocyte, a female germ cell. The medulla is loose connective tissue with abundant blood vessels, lymphatic vessels, and nerve fibers.


Ovarian cysts may be physiological or pathological & may arise from any tissue in the ovary.

Pathology:
Physiological cysts:
Physiological cysts are simply large versions of cysts which form in the ovary during the normal ovarian cycle. Most are asymptomatic incidental findings at pelvic examination or ultrasound scan. They are an occasional complication of ovulation induction, also may occur in premature female infants & in women with trophoblastic disease.

Follicular cyst:
It results from non-rupture of a dominant follicle or failure of atresia in a non-dominant follicle. A follicular cyst may persist for several menstrual cycles & may achieve a diameter of up to 10 cm. intervention may be required if symptoms develop or if the cyst does not resolve after 8-16 weeks. They may produce estrogen causing menstrual disturbance & endometrial hyperplasia.

Luteal cyst:
Less common than follicular cyst, they are more likely to present with intraperitoneal bleeding, commonly on the right side due to increased intraluminal pressure secondary to ovarian vein anatomy. Corpora lutea are not called luteal cyst unless they are more than 3 cm.


Benign germ cell tumours:
• Dermoid cyst (mature cystic teratoma)
• Mature solid teratoma
Benign epithelial tumours:
• Serous cystadenoma
• Mucinous cystadenoma
• Endometrioid cystadenoma
• Brenner tumours

Benign sex cord stromal tumours:

• Theca cell tumours
• Fibroma


Benign germ cell tumours:
The commonest ovarian tumours seen in women less than 30 years old. They arise from totipotential germ cells, & may therefore contain elements of all three germ layers (embryonic differentiation). Differentiation into extra-embryonic tissues results in ovarian choriocarcinoma or endodermal sinus tumour. When neither embryonic nor extra-embryonic differentiation occurs, a dysgerminoma results.

Dermoid cyst (mature cystic teratoma): the most common type. It results from differentiation into embryonic tissues. It account for 40% of all ovarian neoplasms.
A dermoid cyst is usually unilocular, < 15 cm in diameter, in which ectodermal structures are predominant. It is often lined with epithelium like the epidermis & contains skin appendages, teeth, sebaceous material, hair & nervous tissue. Endodermal derivatives include thyroid, bronchus & intestine & the mesoderm may be represented by bone, cartilage & smooth muscle.
Occasionally a single tissue may be present, in which case the term monodermal teratoma is used. The classic example is struma ovarii which contains hormonally active thyroid tissue. A small percentage of struma ovarii produce sufficient thyroid hormone to cause hyperthyroidism & 5-10% of them develop into carcinoma.
The majority of dermoid cysts are asymptomatic. A small percentage may undergo torsion or may rupture spontaneously, either suddenly, causing an acute abdomen & chemical peritonitis; or slowly causing chronic granulomatous peritonitis. As the latter may also follow intraoperative spillage, great care should be taken to avoid this event & thorough peritoneal lavage must be done if it occurs. During pregnancy rupture is more common due to pressure from the expanding uterus or to trauma during delivery.
About 2% contain malignant component, usually squamous carcinoma in women over 40 years old. Again in women less than 20 years 80% of ovarian malignancies are due to germ cell tumours.

Mature solid teratoma:
These rare tumours contain mature tissues just like dermoid cyst, but there are few cystic areas.